A modular multilevel converter representing a conventional power conversion device includes a plurality of arms and a reactor connected in series to each arm. Each arm includes a plurality of cascaded unit cells. Each unit cell has a capacitor charged to a DC voltage and outputs a voltage across terminals of the capacitor or 0 V owing to a switching element. By controlling the switching element of each unit cell in each arm, any one of DC power and AC power can be converted to the other (see, for example, PTD 1 (Japanese National Patent Publication No. 2009-506736), PTD 2 (Japanese Patent Laying-Open No. 2010-233411), and PTD 3 (Japanese Patent Laying-Open No. 2013-115837)).